A general inner rotor type electronic motor includes: a stator that has a cylindrical stator core having a plurality of teeth parts integrally projecting from the inside peripheral surface of a ring-shaped yoke part toward the center and has an insulator surrounding the teeth parts leaving at least a teeth surface of the stator core open; and a rotor that is disposed coaxially in the center of the stator.
One approach for increasing the power output and efficiency of the inner rotor type electronic motor of this type is to increase the diameter of the rotor. Increasing the diameter of rotor, however, increases the diameter of the stator accordingly in the conventional art, which in turn increases the size of the entire electronic motor.
Accordingly, one approach for increasing the size of rotor with the outside dimension of stator being unchanged, is to reducing the thickness in the radial direction of the yoke part of the stator core to enlarge the inside diameter of stator. Reducing the thickness of the yoke part of stator core to thin the stator core, however, poses a problem as described below in a process of winding a coil on the stator.
For example, the conventional stator core has been formed so as to have a slightly large diameter in such a manner that the yoke part has a thickness larger in the radial direction and the outside peripheral surface of the yoke part protrudes to the outside from the outside diameter of the insulator.
Accordingly, when the coil is wound on the stator core, the stator core is positioned while the stator core is brought into contact with a washer provided on the winding machine side using the portion protruding to the outside of the stator core as a reference plane for the positioning.
Therefore, if a thinned stator is used, this reference plane could not be available, which means that positioning cannot be performed at the time of coil winding. It is conceivable to hold and secure the outside peripheral surface of the stator core. However, the outside peripheral surface has not usually been held because the stator core has a relatively low rigidity.
The present invention has been made to solve the above problems, and accordingly an object thereof is to provide an electronic motor in which a stator core is thinned to obtain an increased diameter of a rotor to produce a high power output, and a stator can be positioned with high accuracy at the time when a coil is wound on the stator.